THE CONNECTIVE TISSUES. 



extremities of the diaphysis (in a long bone), and is always preceded 

 as at the center of ossification, by the characteristic structural 

 changes above described. Beginning at the center of ossification and 

 proceeding toward either extremity of the diaphysis, the enlarged and 

 vesicular cartilage-cells will be observed to be arranged in quite reg- 

 ular columns, separated by septa or tra- 

 beculae of calcified cartilage matrix. The 

 cells thus arranged in columns show the 

 degenerative changes above described. 

 They are shrunken and flattened, and 

 their nuclei, when seen, stain less deeply 

 than the nuclei of normal cartilage-cells. 

 Beyond this zone of columns of altered 

 cartilage -cells are found smaller or larger 

 groups of less changed cartilage-cells, 

 and beyond this zone, hyaline cartilage. 



The arrangement of the cartilage- 

 cells in the columns above mentioned is, 

 according to Schiefferdecker, mainly due 

 to two factors the current of lymph 

 plasma which flows from the center of 

 ossification toward the two extremities of 

 the cartilage fundament, and the mutual 

 pressure exerted by the groups of carti- 

 lage-cells in their growth and prolifera- 

 tion. Ossification proceeds from the cen- 

 ter of the diaphysis toward its two ex- 

 tremities by a growth of osteoblasts and 

 small vessels into the columns of carti- 

 lage-cells. Here, also, these degenerate, 

 leaving in their stead irregular, oblong, 

 anastomosing spaces, separated by septa 

 and trabeculae of calcified cartilage ma- 

 trix on which the osteoblasts arrange 

 themselves in layers, and which they 

 envelop in osseous tissue. In a longi- 

 tudinal section of a long bone, preformed 

 in cartilage, the various steps of endo- 

 chondral bone-development may, there- 

 fore, be observed by viewing the prepa- 

 ration from either end to the center of the 

 diaphysis, as may be seen in figures 86, 

 87. The former represents the appear- 

 ance as seen under low magnification, the latter a small portion of 

 such a section fr6m the area of ossification, more highly magnified. 



Adjoining the primary marrow spaces is vesicular cartilage 

 and columns and groups of cartilage-cells and finally hyaline car- 

 tilage. 



Fig. 87. Longitudinal sec- 

 tion through area of ossification 

 from long bone of human em- 

 bryo. 



